More metadata for machines-citations, relations, and preprints arrive in the REST API

Over the past few months we have been adding to the metadata and functionality of our REST API, Crossref’s public machine interface for the metadata of all 90 million+ registered content items. Much of the work focused on a review and upgrade of the API’s code and architecture in order to better support its rapidly growing usage. But we have also extended the types of metadata that the API can deliver.

One of the biggest changes is that references are now available if the publisher has made them public (a simple email instruction to us). Currently 45% of all publications with deposited references are now accessible. For example:

This article studying fluid ejection from animals has 55 references and they are all in the metadata here. You can also see that the article has an is-referenced-by count of 6.

We recently announced that we would be accepting preprints, and the metadata for 15,000 preprints registered to date is now in the API, labelled as posted-content. Over 4,000 have been subsequently published in a journal, and the Crossref metadata now links these preprints to their respective articles (and vice versa). For example this article in Biorxiv has since been published in a journal, and this relationship is recorded in its metadata as is-preprint-of.

Also new to the API:

Cited-by counts - the number of times each work has been referenced by other content registered with us. Look for is-referenced-by-count within a record.

This article from 1953 about a fairly notable discovery has been cited 4832 times, but the two mostcited articles both have over 100,000 citations and thousands have been cited more than Watson and Crick.